The two are different oils. The SAF-XJ is the standard oil we install during all 1200 mile services. We carry it in a 55 gallon drum. I verified all part numbers before performing my own 1200 mile service. I just wanted to be certain we were using the correct oil. This is the standard oil listed by BMW in the "operating fluids" section of BMW's technical information. This oil is also available as a 1 litre bottle, part# 83 22 1 467 993.

The "specially formulated differential oil" (83 22 2 282 583) is the fluid listed in the Service Bulletin to use when the regular SAF-XJ oil results in excessive clutch noise. I know this because I have performed this bulletin on several cars. This oil contains additional friction modifiers to reduce noise.

Although I know they are different oils, I can provide you with one particular incident that stands out in my mind. I have an E90 M3 customer that asks for me to personally work on his car whenever he needs service. I performed the run-in service on his car right around 1000 miles, using the SAF-XJ oil in the 55 gallon drum. A few weeks later, he comes in to talk to me about a loud rubbing noise he is hearing while turning into his driveway. I tell him it is most likely the clutch pack in the rear diff. After a test drive, it is certainly the differential, and it was LOUD. I drained the SAF-XJ oil and filled the diff with the special #583 oil. A quick road test later and the noise was completely gone. This is enough to prove to me that these are different oils.

I could be completely wrong, but having first hand experience with this stuff for years, I really don't think so. I am not trying to be argumentative; I just want people to be getting the most accurate info.